Don’t believe the mike: Behavioural, directional, and environmental impacts on recorded bat echolocation call measures

Echolocation calls produced by bats in their larynges allow these flying, nocturnal mammals to orient and find food at night. The acoustic signals are not like bird song, and even individual bats exhibit great flexibility in call design and between-species overlap is common. As a result, identifying bats to species by their echolocation calls even in communities with few bat species can be difficult. Unfortunately, the situation is worse still. As a result of several factors - some to do with microphones, some with environment, some with bats, and the calls themselves - acoustic information transmitted to and transduced by microphones can be dramatically different from the actual signal produced by the bat and as would be recorded on axis, close to its mouth using ideal microphones under ideal conditions. We outline some of these pitfalls and discuss ways to make the best of a bad situation. Overall, however, we stress that many of these factors cannot be ignored and do impact our recordings.